Reduction-order Modeling And Maximum Power Point Tracking Control Of High-voltage-gain Converter For Photovoltaic System

The output characteristics of photovoltaic power generation system are affected easily by the external environment,which is nonlinear and intermittent.In order to realize the maximum utilization of solar energy,it is necessary to control the nonlinear photovoltaic output with maximum power point tracking(MPPT).In addition,the output voltage of photovoltaic system is low,so a high-gain DC-DC converter is required to boost the voltage to interface the power grid.In the existing converters,single-stage multi-cell high-order DC-DC converter has been widely used for its advantages,i.e.,high power density,low cost and high efficiency.However,with the increased number of units,the number of switching variables and dynamic components in the multi-cell converter also increases,which leads to the high order feature of the system,and thus the control complexity.In view of control theory,only when the controllability of the converter is obtained,then the control performance can be monitored and adjusted.In addition,new requirements are put forward for the response speed and control precision of the higher-order system,which also brings great difficulties to its stable transient and steady-state response.Therefore,it is urgent to achieve order reduction modeling and high-performance maximum power tracking control for high-order photovoltaic systems.(1)The switching linear system mathematical model is established for the high-order single-stage multi-cell DC-DC converter.Then,its controllability is developed from the perspective of graph theory and matrix criterion respectively,so as to verify the feasibility of the high-gain converter in the power conversion of photovoltaic system.(2)Based on the theory of state space,the parameter averaging based modeling(PAM)of high-order power converter is established to achieve the establishment of the system’s loworder model,so as to reduce the computational complexity and workload of calculating the steady-state operating point and transfer function,and achieve fast and stable maximum power tracking control.(3)Based on the PAM model,the closed-loop control design of the high-order photovoltaic power generation system is carried out to realize the maximum power tracking control with fast control response.The PAM reduced order model is verified by the light intensity drops sharply experiment,and the experimental results show that the proposed model can run fast and stable MPPT control for the high gain DC-DC converter.Creativities of this dissertation include:(1)controllability of high order converters including practical control strategy design and topology structure are analyzed through the controllability theory;(2)A reduced order model derived from the high order model is established to realize the rapid and stable control.These creativities can be a guideline both in theory and application for high-order converters of photovoltaic system.